Peugeot 405 Manual

Cooling system electrical switches and sensors - testing, removal and refitting
Cooling, heating and ventilation systems / Cooling system electrical switches and sensors - testing, removal and refitting


Electric cooling fan thermostatic switch - models without air conditioning
Testing
1 Testing of the switch is described in Section 5, as part of the electric cooling fan test procedure.

Removal
2 The switch is located in the left-hand side of the radiator. The engine and radiator should be cold before removing the switch.

3 Disconnect the battery negative lead.

4 Partially drain the cooling system to just below the level of the switch (see Chapter 1).

Alternatively, have ready a suitable bung to plug the switch aperture in the radiator when the switch is removed. If this method is used, take great care not to damage the radiator, and do not use anything which will allow foreign matter to enter the radiator.

5 Disconnect the wiring plug from the switch.

6 Carefully unscrew the switch from the radiator, and recover the sealing ring. If the system has not been drained, plug the switch aperture to prevent further coolant loss.

Refitting
7 Refitting is a reversal of removal, using a new sealing ring. Tighten the switch, and refill (or top-up) the cooling system (see Chapter 1).

8 On completion, start the engine and run it until it reaches normal operating temperature.

Continue to run the engine, and check that the cooling fan cuts in and out correctly.

Electric cooling fan thermostatic switch - models with air conditioning
9 On most models fitted with air conditioning, the cooling fans are controlled by the Bitron sensor. This is located in the thermostat housing, and is described in more detail later in this Section.

10 On some later models with air conditioning, the cooling fan(s) is/are controlled by a switch mounted in the radiator, as described previously for models without air conditioning. It will be self-evident which type of switch is used. If no switch is fitted to the radiator, the Bitron sensor is used to control the fan(s).

Coolant temperature gauge/ temperature warning light sender
Testing
11 The coolant temperature gauge/warning light sender is screwed into the thermostat housing.

12 The temperature gauge (where fitted) is fed with a stabilised voltage from the instrument panel feed (via the ignition switch and a fuse). The gauge earth is controlled by the sender. The sender contains a thermistor - an electronic component whose electrical resistance decreases at a predetermined rate as its temperature rises. When the coolant is cold, the sender resistance is high, current flow through the gauge is reduced, and the gauge needle points towards the blue (cold) end of the scale. As the coolant temperature rises and the sender resistance falls, current flow increases, and the gauge needle moves towards the upper end of the scale. If the sender is faulty, it must be renewed.

13 On models with a temperature warning light, the light is fed with a voltage from the instrument panel. The light earth is controlled by the sender. The sender is effectively a switch, which operates at a predetermined temperature to earth the light and complete the circuit. If the light is fitted in addition to a gauge, the senders for the gauge and light are incorporated in a single unit, with two wires, one each for the light and gauge earths. On models with air conditioning, the light is operated via the Bitron sensor - see paragraphs 19 to 21.

14 If the gauge develops a fault, first check the other instruments; if they do not work at all, check the instrument panel electrical feed.

If the readings are erratic, there may be a fault in the voltage stabiliser, which will necessitate renewal of the stabiliser (the stabiliser is integral with the instrument panel printed circuit board - see Chapter 12). If the fault lies in the temperature gauge alone, check it as follows.

15 If the gauge needle remains at the cold end of the scale when the engine is hot, disconnect the sender wiring plug, and earth the relevant wire to the cylinder head. If the needle then deflects when the ignition is switched on, the sender unit is proved faulty, and should be renewed. If the needle still does not move, remove the instrument panel (Chapter 12) and check the continuity of the wire between the sender unit and the gauge, and the feed to the gauge unit. If continuity is shown, and the fault still exists, then the gauge is faulty, and the gauge unit should be renewed.

16 If the gauge needle remains at the hot end of the scale when the engine is cold, disconnect the sender wire. If the needle then returns to the cold end of the scale when the ignition is switched on, the sender unit is proved faulty, and should be renewed. If the needle still does not move, check the remainder of the circuit as described previously.

17 The same basic principles apply to testing the warning light. The light should illuminate when the relevant sender wire is earthed.

Removal and refitting
18 The procedure is similar to that described previously in this Section for the electric cooling fan thermostatic switch. On some models, access to the switch is very poor, and other components may need to be removed before the sender unit can be reached.

Bitron temperature sensor - models with air conditioning Testing
19 The sensor forms part of the air conditioning Bitron control system (see Section 11). Testing of the sensor should be entrusted to a Peugeot dealer.

Removal and refitting
20 The Bitron temperature sensor is screwed into the thermostat housing, which is bolted onto the left-hand end of the cylinder head.

21 The procedure is similar to that described previously in this Section for the electric cooling fan thermostatic switch. On some models, access to the switch is very poor, and other components may need to be removed before the sender unit can be reached.

Coolant temperature sensor - fuel injection models
Testing
22 The fuel injection system coolant temperature sensor is screwed into the thermostat housing, which is bolted onto the left-hand end of the cylinder head.

23 The sensor is a thermistor (see paragraph 12). The fuel injection/engine management electronic control unit (ECU) supplies the sensor with a set voltage and then, by measuring the current flowing in the sensor circuit, it determines the engines temperature. This information is then used, in conjunction with other inputs, to control the injector opening time (pulse width). On some models, the idle speed and/or ignition timing settings are also temperature-dependent.

24 If the sensor circuit should fail to provide adequate information, the ECUs back-up facility will override the sensor signal. In this event, the ECU assumes a predetermined setting which will allow the fuel injection/engine management system to run, albeit at reduced efficiency. When this occurs, the warning light on the instrument panel will come on, and the advice of a Peugeot dealer should be sought. The sensor itself can only be tested using special Peugeot diagnostic equipment. Do not attempt to test the circuit using any other equipment, as there is a high risk of damaging the ECU.

Removal and refitting
25 The procedure is similar to that described previously in this Section for the electric cooling fan thermostatic switch. On some models, access to the switch is very poor, and certain components may need to be removed before the sensor can be reached.


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